Surgical needles and methods of manufacturing surgical needles are well known in the art. Surgical needles are typically manufactured from biocompatible alloys such as 300 and 400 series stainless steels (stainless steel alloys), and the like. It is also known to manufacture surgical needles from polymeric materials, ceramics, and composites. Metal alloy surgical needles are manufactured using a variety of manufacturing processes. Typically, a metal alloy is drawn into a wire using a conventional wire drawing process using dies. The wire is then cut into discreet needle blanks. The needle blanks are the precursors of the surgical needles and undergo a series of conventional mechanical, thermal and chemical processes and treatments in order to be formed into a finished surgical needle suitable for mounting to a conventional surgical suture. The mechanical processes include straightening, curving, coining, grinding, and the like. The thermal processes include heat treating, age hardening, annealing and the like. The chemical processes include passivation, polishing, etching, coloring, and the like.
Surgical needles require a variety of requisite mechanical properties and characteristics in order to function optimally when used in surgical procedures. Since surgical needles and attached sutures are used to approximate or join tissue, these characteristics include ease of penetration through tissue, sharpness of needle points, stiffness, yield strength, ultimate strength, ductility, biocompatibility, etc.
There has been increased interest in this art for surgical needles having improved bending stiffness. Bending stiffness is particularly important for curved surgical needles so that a needle maintains its shape when subjected to forces as the surgeon moves the needle through tissue. Accordingly, there has been interest in this art to manufacture surgical needles from refractory alloy materials. Examples of such refractory alloy materials include tungsten rhenium alloys (W—Re). It is known that W—Re alloys exhibit exceptionally high Young's Moduli in excess of 400 GPa.
However, when formed into a curved suture needle this exceptional resistance to elastic deformation is reduced substantially. When an “unbending” moment is applied to the curved needle, plastic deformation initiates at relatively low applied stresses.
There have been numerous attempts to improve the bending stiffness of surgical needles. Although such approaches may have produced relative degrees of improvement, these approaches have not been shown to enhance the bending stiffness of W—Re surgical needles. For example, precipitation strengthened steel alloys have been used to maximize bending stiffness of ferrous needles. The configuration of surgical needles has been changed to incorporate various forms of rectangular geometries in order to gain an increase in bending stiffness. Another approach that has been used is the use of oversized large surgical steel needles with relatively small sutures to enhance stiffness in bending. Yet another way of attempting to improve bending stiffness is to select specific types of alloys with high moduli.
Accordingly, there is a need in this art for improved surgical needles made from metal alloys, in particular tungsten alloys, that are significantly stiffer than conventional curved stainless steel needles and which have improved characteristics in comparison to other tungsten alloy needles.